Maximum Attainable Wheat Yield: What Is the Limit in the Southern Great Plains?.

Maximum reported grain yields for hard red winter wheat (Triticum aestivum L.) in the southern Great Plains (SGP) range from 6 to 8 Mg ha^-1 and are significantly lower than yields achieved in other regions of the world. The lack of empirical data for wheat under non-limiting conditions in the SGP, however, suggests that maximum reported grain yields for the region might not represent maximum attainable yields. The objective of this research was to perform the agronomic characterization of winter wheat grown under non-limiting conditions across the SGP. Four dryland and two irrigated fields were sown to ‘Iba’ winter wheat in the growing seasons of 2012-13 and 2013-14 in central Oklahoma. Fields were intensively managed to provide adequate fertility for maximum yield and freedom from weeds, insects, and disease. Aboveground dry matter, fractional canopy cover, leaf area index, and soil water content, were measured at approximately two-week intervals for a complete characterization of soil-plant-atmosphere dynamics. Although aboveground dry matter at maturity ranged from 9.95 to 20.49 Mg ha^-1 among locations and years, harvest index values did not surpass 40.9 and grain yields ranged from 3061 to 7677 kg ha^-1. The highest yield was achieved under irrigated conditions in 2013-14, but one dryland site produced a 7111 kg ha^-1 grain yield the previous year. Seasonal crop evapotranspiration ranged from 303 to 720 mm, and was highly correlated with grain yield (R² = 0.82). Radiation use efficiency ranged from 1.6 to 2.6 g MJ ha^-1 and water productivity from 11.2 to 23.2 g mm^-1. The wheat agronomic characteristics observed in this study were near or above maximum values reported in the literature for the SGP, and our data provide empirical evidence to support winter wheat yields as high as 7677 kg ha^-1 when grown under non-limiting conditions in the SGP.